This is a resubmitted application requesting support for the continuation of a highly successful and well-established postdoctoral training program in molecular imaging and cancer systems analysis, a program that is currently in its tenth year. Currently, there are very few broad, in- depth and interdisciplinary training opportunities that enable individuals to develop and validate novel and non-invasive methods for detecting molecular and cellular processes in vivo, and which could ultimately be used in patients. Such a training program exists at the Center for Systems Biology at Massachusetts General Hospital and includes members of the two NIH- designated Cancer Centers as well as faculty at Harvard Medical School and at Massachusetts Institute of Technology. This training grant is in its tenth year of funding and has had a total of 30 trainees (four trainee positions in years 1-5, six trainee positions thereafter). Twenty five trainees have graduated from the program, the majority of which are now in academia. Overall, trainees have published over 130 peer-reviewed publications to date. The faculty (34 members) are highly accomplished and currently receive over 250 extramural research grants. In the past several years, this training program has had many more applicants than it has been able to accommodate. The curriculum, which includes formal courses, laboratory exercises and individual research projects, is firmly established and trainee research is regularly monitored by their preceptors. Successful programs have also been developed for recruitment of underrepresented minorities and women, scientific integrity and for cancer-related training and research. More recently, the training program has been considerably strengthened by a move to new research facilities, the introduction of a new Chemical Biology Program, the implementation of a computational program in addition to an expanded imaging facility. With our current faculty, enhanced facilities, scope of supported research and past accomplishments, we offer an outstanding research environment for the next generation of clinicians and scientists to be trained in molecular imaging and systems analysis.